The manufacturing process of a semiconductor integrated circuit typically includes a series of processes for depositing conductive layers and insulating layers on the entire surface of a semiconductor wafer and patterning the material layers forming each layer to realize the semiconductor integrated circuit as designed.
In general, a semiconductor integrated circuit includes a plurality of units of semiconductor chips formed by carrying out the same processes in the same steps with respect to the plurality of semiconductor chips on the semiconductor wafer. Thus, after forming an uppermost material layer on each semiconductor chip unit, the semiconductor wafer is diced into the semiconductor chips and end parts thereof are discarded as unnecessary portions.
Because the manufacturing process for the semiconductor device is typically carried out relative to the entire surface of a semiconductor wafer, the material layers tend to form on the edge of the semiconductor wafer. However, the edge of the semiconductor wafer is an imperfect region in terms of crystallization, energy distribution, and mechanical strength, so the edge of the semiconductor wafer causes various defects in the process of forming the semiconductor integrated circuit.
That is, as semiconductor integrated circuits have become highly integrated, material layers accumulated on the edge and the bevel region of the wafer may cause various types of defects, such as expansion due to a thermal budget derived from, for example, deposition of a subsequent material layer, a lifting of a material layer, an incomplete removal of a material layer caused by a difference of selectivity between layers relative to a chemical used in dry etching or wet etching, and polymer residue. Such defects may generate particles, which penetrate into a semiconductor chip region in the process of manufacturing the semiconductor integrated circuit, thereby causing defects of the semiconductor integrated circuit.
Therefore, the material layers formed on an edge of the wafer have to be periodically removed therefrom during the manufacturing process for the semiconductor integrated circuit.
FIGS. 1 and 2 show a conventional method for processing a wafer edge.
Referring to FIG. 1, a tungsten silicide layer or a tungsten layer 61, a silicon nitride layer 62 and a silicon oxide layer 63 are formed on an edge of a wafer 60 in a process of manufacturing a semiconductor integrated circuit.
In order to remove such unnecessary material layers formed on the edge of the wafer 60, in a conventional process, a photoresist layer 64 is coated on the entire surface of the wafer 60 including a semiconductor chip region (not shown) and then a pattern of the photoresist layer 64 having a regular width is formed from the edge of the wafer 60 through a photo process.
Referring to FIG. 2, the silicon oxide layer 63 exposed at the edge and a rear side of the wafer 60 is removed by a wet chemical etch using the photoresist layer 64 as a mask. Then, the photoresist layer 64 is removed by ashing and stripping processes.
After that, the exposed silicon nitride layer 62 is removed by using an appropriate chemical while employing the silicon oxide layer 63 as a mask. Subsequently, the exposed tungsten silicide layer or tungsten layer 61 is removed.
However, the conventional method does not completely remove the silicon oxide layer 63 from the edge and a lower region of the wafer 60. Instead, the residue of the silicon oxide layer 63 may remain on the edge and the lower region of the wafer 60.
Therefore, it is necessary to ensure that the silicon oxide layer or other material layers remaining on the edge and the lower region of the wafer are removed.